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We tested the role of descending projections forauditory processing and audiomotor integration in the anuran torus semicircularis.Intracellular recordings were made from isolated brain preparations, impaledneurons were stained. Auditory neurons responded to electrical stimulationof striatum and/or dorsal thalamus, they integrated forebrain and auditorynerve inputs. High frequency stimulation in striatum or thalamus changed theauditory response of torus neurons located in the laminar subnucleus. Ourresults suggest that the laminar nucleus is the primary target of forebrainprojections, which provides a basis for modulation of acoustically guidedbehaviour. [ABSTRACT FROM AUTHOR]

Degeneration of dopaminergic neurons in the substantia nigra and their striatal axon terminals causes cardinal motor symptoms of Parkinson's disease. In idiopathic cases, high levels of mitochondrial DNA alterations, leading to mitochondrial dysfunction, are a central feature of these vulnerable neurons. Here we present a mouse model expressing the K320E variant of the mitochondrial helicase Twinkle in dopaminergic neurons, leading to accelerated mitochondrial DNA mutations. These K320E-TwinkleDaN mice showed normal motor function at 20 months of age, although ∼70% of nigral dopaminergic neurons had perished. Remaining neurons still preserved ∼75% of axon terminals in the dorsal striatum and enabled normal dopamine release. Transcriptome analysis and viral tracing confirmed compensatory axonal sprouting of the surviving neurons. We conclude that a small population of substantia nigra dopaminergic neurons is able to adapt to the accumulation of mitochondrial DNA mutations and maintain motor control., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Mutations of isocitrate dehydrogenase 1 (IDH1) are key biomarkers for glioma classification, but current methods for detection of mutated IDH1 (mIDH1) require invasive tissue sampling and cannot be used for longitudinal studies. Positron emission tomography (PET) imaging with mIDH1-selective radioligands is a promising alternative approach that could enable non-invasive assessment of the IDH status. In the present work, we developed efficient protocols for the preparation of four 18 F-labeled derivatives of the mIDH1-selective inhibitor olutasidenib. All four probes were characterized by cellular uptake studies with U87 glioma cells harboring a heterozygous IDH1 mutation (U87-mIDH) and the corresponding wildtype cells (U87-WT). In addition, the most promising probe was evaluated by PET imaging in healthy mice and mice bearing subcutaneous U87-mIDH and U87-WT tumors. Although all four probes inhibited mIDH1 with variable potencies, only one of them ([ 18 F]mIDH-138) showed significantly higher in vitro uptake into U87-mIDH compared to U87-WT cells. In addition, PET imaging with [ 18 F]mIDH-138 in mice demonstrated good in vivo stability and low non-specific uptake of the probe, but also revealed significantly higher uptake into U87-WT compared to U87-mIDH tumors. Finally, application of a two-tissue compartment model (2TCM) to the PET data indicated that preferential tracer uptake into U87-WT tumors results from higher specific binding rather than from differences in tracer perfusion. In conclusion, these results corroborate recent findings that mIDH1-selective inhibition may not directly correlate with mIDH1-selective target engagement and indicate that in vivo engagement of wildtype and mutated IDH1 may be governed by factors that are not faithfully reproduced by in vitro assays, both of which could complicate development of PET probes.

Compensatory changes in brain connectivity keep motor symptoms mild in prodromal Parkinson's disease. Studying compensation in patients is hampered by the steady progression of the disease and a lack of individual baseline controls. Furthermore, combining fMRI with walking is intricate. We therefore used a seed-based metabolic connectivity analysis based on 2-deoxy-2-[ 18 F]fluoro-D-glucose ([ 18 F]FDG) uptake in a unilateral 6-OHDA rat model. At baseline and in the chronic phase 6-7 months after lesion, rats received an intraperitoneal injection of [ 18 F]FDG and spent 50 min walking on a horizontal treadmill, followed by a brain PET-scan under anesthesia. High activity was found in the cerebellar anterior vermis in both conditions. At baseline, the anterior vermis showed hardly any stable connections to the rest of the brain. The (future) ipsilesional cerebellar hemisphere was not particularly active during walking but was extensively connected to many brain areas. After unilateral dopamine depletion, rats still walked normally without obvious impairments. The ipsilesional cerebellar hemisphere increased its activity, but narrowed its connections down to the vestibulocerebellum, probably aiding lateral stability. The anterior vermis established a network involving the motor cortex, hippocampus and thalamus. Adding those regions to the vermis network of (previously) automatic control of locomotion suggests that after unilateral dopamine depletion considerable conscious and cognitive effort has to be provided to achieve stable walking.

O -([ 18 F]Fluoroethyl)-l-tyrosine ([ 18 F]FET) is actively transported into the brain and cancer cells by LAT1 and possibly other amino acid transporters, which enables brain tumor imaging by positron emission tomography (PET). However, tumor delivery of this probe in the presence of competing amino acids may be limited by a relatively low affinity for LAT1. The aim of the present work was to evaluate the meta -substituted [ 18 F]FET analog m -[ 18 F]FET and the methyl ester [ 18 F]FET-OMe, which were designed to improve tumor delivery by altering the physicochemical, pharmacokinetic, and/or transport properties. Both tracers could be prepared with good radiochemical yields of 41-56% within 66-90 min. Preclinical evaluation with [ 18 F]FET as a reference tracer demonstrated reduced in vitro uptake of [ 18 F]FET-OMe by U87 glioblastoma cells and no advantage for in vivo tumor imaging. In contrast, m -[ 18 F]FET showed significantly improved in vitro uptake and accelerated in vivo tumor accumulation in an orthotopic glioblastoma model. As such, our work identifies m -[ 18 F]FET as a promising alternative to [ 18 F]FET for brain tumor imaging that deserves further evaluation with regard to its transport properties and in vivo biodistribution.

Concussion, caused by a rotational acceleration/deceleration injury mild enough to avoid structural brain damage, is insufficiently captured in recent preclinical models, hampering the relation of pathophysiological findings on the cellular level to functional and behavioral deficits. We here describe a novel model of unrestrained, single vs. repetitive concussive brain injury (CBI) in male C56Bl/6j mice. Longitudinal behavioral assessments were conducted for up to seven days afterward, alongside the evaluation of structural cerebral integrity by in vivo magnetic resonance imaging (MRI, 9.4 T), and validated ex vivo by histology. Blood-brain barrier (BBB) integrity was analyzed by means of fluorescent dextran- as well as immunoglobulin G (IgG) extravasation, and neuroinflammatory processes were characterized both in vivo by positron emission tomography (PET) using [ 18 F]DPA-714 and ex vivo using immunohistochemistry. While a single CBI resulted in a defined, subacute neuropsychiatric phenotype, longitudinal cognitive testing revealed a marked decrease in spatial cognition, most pronounced in mice subjected to CBI at high frequency (every 48 h). Functional deficits were correlated to a parallel disruption of the BBB, (R 2 = 0.29, p < 0.01), even detectable by a significant increase in hippocampal uptake of [ 18 F]DPA-714, which was not due to activation of microglia, as confirmed immunohistochemically. Featuring a mild but widespread disruption of the BBB without evidence of macroscopic damage, this model induces a characteristic neuro-psychiatric phenotype that correlates to the degree of BBB disruption. Based on these findings, the BBB may function as both a biomarker of CBI severity and as a potential treatment target to improve recovery from concussion.

The DSL-6A/C1 murine pancreatic ductal adenocarcinoma (PDAC) tumor model was established in Lewis rats and characterized through a comprehensive multiparametric analysis to compare it to other preclinical tumor models and explore potential diagnostic and therapeutical targets. DSL-6A/C1 tumors were histologically analyzed to elucidate PDAC features. The tumor microenvironment was studied for immune cell prevalence. Multiparametric MRI and PET imaging were utilized to characterize tumors, and 68 Ga-FAPI-46-targeting cancer-associated fibroblasts (CAFs), were used to validate the histological findings. The histology confirmed typical PDAC characteristics, such as malformed pancreatic ductal malignant cells and CAFs. Distinct immune landscapes were identified, revealing an increased presence of CD8 + T cells and a decreased CD4 + T cell fraction within the tumor microenvironment. PET imaging with 68 Ga-FAPI tracers exhibited strong tracer uptake in tumor tissues. The MRI parameters indicated increasing intralesional necrosis over time and elevated contrast media uptake in vital tumor areas. We have demonstrated that the DSL-6A/C1 tumor model, particularly due to its high tumorigenicity, tumor size, and 68 Ga-FAPI-46 sensitivity, is a suitable alternative to established small animal models for many forms of preclinical analyses and therapeutic studies of PDAC.

In a previous study, regional reductions in cerebral glucose metabolism have been demonstrated in the tauopathy mouse model rTg4510 (Endepols et al., 2022). Notably, glucose hypometabolism was present in some brain regions without co-localized synaptic degeneration measured with [ 18 F]UCB-H. We hypothesized that in those regions hypometabolism may reflect reduced functional connectivity rather than synaptic damage. To test this hypothesis, we performed seed-based metabolic connectivity analyses using [ 18 F]FDG-PET data in this mouse model. Eight rTg4510 mice at the age of seven months and 8 non-transgenic littermates were injected intraperitoneally with 11.1 ± 0.8 MBq [ 18 F]FDG and spent a 35-min uptake period awake in single cages. Subsequently, they were anesthetized and measured in a small animal PET scanner for 30 min. Three seed-based connectivity analyses were performed per group. Seeds were selected for apparent mismatch between [ 18 F]FDG and [ 18 F]UCB-H. A seed was placed either in the medial orbitofrontal cortex, dorsal hippocampus or dorsal thalamus, and correlated with all other voxels of the brain across animals. In the control group, the emerging correlative pattern was strongly overlapping for all three seed locations, indicating a uniform fronto-thalamo-hippocampal resting state network. In contrast, rTg4510 mice showed three distinct networks with minimal overlap. Frontal and thalamic networks were greatly diminished. The hippocampus, however, formed a new network with the whole parietal cortex. We conclude that resting-state functional networks are fragmented in the brain of rTg4510 mice. Thus, hypometabolism can be explained by reduced functional connectivity of brain areas devoid of tau-related pathology, such as the thalamus., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: The TgF344-AD ratline represents a transgenic animal model of Alzheimer's disease. We previously reported spatial memory impairment in TgF344-AD rats, yet the underlying mechanism remained unknown. We, therefore, set out to determine if spatial memory impairment in TgF344-AD rats is attributed to spatial disorientation. Also, we aimed to investigate whether TgF344-AD rats exhibit signs of asymmetry in hemispheric neurodegeneration, similar to what is reported in spatially disoriented AD patients. Finally, we sought to examine how spatial disorientation correlates with working memory performance., Methods: TgF344-AD rats were divided into two groups balanced by sex and genotype. The first group underwent the delayed match-to-sample (DMS) task for the assessment of spatial orientation and working memory, while the second group underwent positron emission tomography (PET) for the assessment of glucose metabolism and microglial activity as in-vivo markers of neurodegeneration. Rats were 13 months old during DMS training and 14-16 months old during DMS testing and PET., Results: In the DMS task, TgF344-AD rats were more likely than their wild-type littermates to display strong preference for one of the two levers, preventing working memory testing. Rats without lever-preference showed similar working memory, regardless of their genotype. PET revealed hemispherically asymmetric clusters of increased microglial activity and altered glucose metabolism in TgF344-AD rats., Conclusions: TgF344-AD rats display spatial disorientation and hemispherically asymmetrical neurodegeneration, suggesting a potential causal relationship consistent with past clinical research. In rats with preserved spatial orientation, working memory remains intact., Competing Interests: The authors have no conflict of interest to report., (© 2023 – The authors. Published by IOS Press.)

18 F-Fluorination of sensitive molecules is often challenging, but can be accomplished under suitably mild conditions using radiofluorinated prosthetic groups (PGs). Herein, 1-alkylamino-7-[ 18 F]fluoro-8-azaisatoic anhydrides ([ 18 F]AFAs) are introduced as versatile 18 F-labeled building blocks that can be used as amine-reactive or "click chemistry" PGs. [ 18 F]AFAs were efficiently prepared within 15 min by "on cartridge" radiolabeling of readily accessible trimethylammonium precursors. Conjugation with a range of amines afforded the corresponding 2-alkylamino-6-[ 18 F]fluoronicotinamides in radiochemical conversions (RCCs) of 15-98%. In addition, radiolabeling of alkyne- or azide-functionalized precursors with azidopropyl- or propargyl-substituted [ 18 F]AFAs using Cu-catalyzed click cycloaddition afforded the corresponding conjugates in RCCs of 44-88%. The practical utility of the PGs was confirmed by the preparation of three 18 F-labeled PSMA ligands in radiochemical yields of 28-42%. Biological evaluation in rats demonstrated excellent in vivo stability of all three conjugates. In addition, one conjugate ([ 18 F]JK-PSMA-15) showed favorable imaging properties for high-contrast visualization of small PSMA-positive lesions.

Introduction: The primary compounds of Cannabis sativa , delta-9-tetrahydrocannabinol (Δ 9 -THC) and cannabidiol (CBD), inflict a direct influence on the endocannabinoid system-a complex lipid signaling network with a central role in neurotransmission and control of inhibitory and excitatory synapses. These phytocannabinoids often interact with endogenously produced endocannabinoids (eCBs), as well as their structurally related N -acylethanolamines (NAEs), to drive neurobiological, nociceptive, and inflammatory responses. Identifying and quantifying changes in these lipid neuromodulators can be challenging owing to their low abundance in complex matrices. Materials and Methods: This article describes a robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the extraction and quantification of the eCBs anandamide and 2-arachidonoylglycerol, along with their congener NAEs oleoylethanolamine and palmitoylethanolamine, and phytocannabinoids CBD, Δ 9 -THC, and 11-Nor-9-carboxy-Δ 9 -tetrahydrocannabinol, a major metabolite of Δ 9 -THC. Our method was applied to explore pharmacokinetic and pharmacodynamic effects from intraperitoneal injections of Δ 9 -THC and CBD on circulating levels of eCBs and NAEs in rodent serum. Results: Detection limits ranged from low nanomolar to picomolar in concentration for eCBs (0.012-0.24 pmol/mL), NAEs (0.059 pmol/mL), and phytocannabinoids (0.24-0.73 pmol/mL). Our method displayed good linearity for calibration curves of all analytes ( R 2 >0.99) as well as acceptable accuracy and precision, with quality controls not deviating >15% from their nominal value. Our LC-MS/MS method reliably identified changes to these endogenous lipid mediators that followed a causal relationship, which was dependent on both the type of phytocannabinoid administered and its pharmaceutical preparation. Conclusion: We present a rapid and reliable method for the simultaneous quantification of phytocannabinoids, eCBs, and NAEs in serum using LC-MS/MS. The accuracy and sensitivity of our assay infer it can routinely monitor endogenous levels of these lipid neuromodulators in serum and their response to external stimuli, including cannabimimetic agents.

The accumulation of tau is a hallmark of several neurodegenerative diseases and is associated with neuronal hypoactivity and presynaptic dysfunction. Oral administration of the adenosine A 1 receptor antagonist rolofylline (KW-3902) has previously been shown to reverse spatial memory deficits and to normalize the basic synaptic transmission in a mouse line expressing full-length pro-aggregant tau (Tau ΔK ) at low levels, with late onset of disease. However, the efficacy of treatment remained to be explored for cases of more aggressive tauopathy. Using a combination of behavioral assays, imaging with several PET-tracers, and analysis of brain tissue, we compared the curative reversal of tau pathology by blocking adenosine A1 receptors in three mouse models expressing different types and levels of tau and tau mutants. We show through positron emission tomography using the tracer [ 18 F]CPFPX (a selective A1 receptor ligand) that intravenous injection of rolofylline effectively blocks A 1 receptors in the brain. Moreover, when administered to Tau ΔK mice, rolofylline can reverse tau pathology and synaptic decay. The beneficial effects are also observed in a line with more aggressive tau pathology, expressing the amyloidogenic repeat domain of tau (TauRD ΔK ) with higher aggregation propensity. Both models develop a progressive tau pathology with missorting, phosphorylation, accumulation of tau, loss of synapses, and cognitive decline. TauRD ΔK causes pronounced neurofibrillary tangle assembly concomitant with neuronal death, whereas Tau ΔK accumulates only to tau pretangles without overt neuronal loss. A third model tested, the rTg4510 line, has a high expression of mutant Tau P301L and hence a very aggressive phenotype starting at ~3 months of age. This line failed to reverse pathology upon rolofylline treatment, consistent with a higher accumulation of tau-specific PET tracers and inflammation. In conclusion, blocking adenosine A1 receptors by rolofylline can reverse pathology if the pathological potential of tau remains below a threshold value that depends on concentration and aggregation propensity.

Positron emission tomography (PET) imaging with radiotracers that bind to fibrillary amyloid β (Aβ) deposits is an important tool for the diagnosis of Alzheimer's disease (AD) and for the recruitment of patients into clinical trials. However, it has been suggested that rather than the fibrillary Aβ deposits, it is smaller, soluble Aβ aggregates that exert a neurotoxic effect and trigger AD pathogenesis. The aim of the current study is to develop a PET probe that is capable of detecting small aggregates and soluble Aβ oligomers for improved diagnosis and therapy monitoring. An 18 F-labeled radioligand was prepared based on the Aβ-binding d-enantiomeric peptide RD2, which is currently being evaluated in clinical trials as a therapeutic agent to dissolve Aβ oligomers. 18 F-labeling was carried out using palladium-catalyzed S-arylation of RD2 with 2-[ 18 F]fluoro-5-iodopyridine ([ 18 F]FIPy). Specific binding of [ 18 F]RD2-cFPy to brain material from transgenic AD (APP/PS1) mice and AD patients was demonstrated with in vitro autoradiography. In vivo uptake and biodistribution of [ 18 F]RD2-cFPy were evaluated using PET analyses in wild-type and transgenic APP/PS1 mice. Although brain penetration and brain wash-out kinetics of the radioligand were low, this study provides proof of principle for a PET probe based on a d-enantiomeric peptide binding to soluble Aβ species., Competing Interests: Declaration of Competing Interest A.W. and D.W. are co-founders of Priavoid GmbH, Düsseldorf, Germany. A.W. is a part-time employee, and D.W. is a member of the supervisory board of Priavoid, which develops RD2 as a therapeutic compound. Priavoid holds no intellectual property concerning the development of RD2 as a diagnostic compound. All other authors declare no conflict of interest., (Copyright © 2023. Published by Elsevier B.V.)

Cu-mediated radiofluorination is a versatile tool for the preparation of 18 F-labeled (hetero)aromatics. In this work, we systematically evaluated a series of complexes and identified several generally applicable mediators for highly efficient radiofluorination of aryl boronic and stannyl substrates. Utilization of these mediators in nBuOH/DMI or DMI significantly improved 18 F-labeling yields despite use of lower precursor amounts. Impressively, application of 2.5 μmol aryl boronic acids was sufficient to achieve 18 F-labeling yields of up to 75 %. The practicality of the novel mediators was demonstrated by efficient production of five PET-tracers and transfer of the method to an automated radiosynthesis module. In addition, (S)-3-[ 18 F]FPhe and 6-[ 18 F]FDOPA were prepared in activity yields of 23±1 % and 30±3 % using only 2.5 μmol of the corresponding boronic acid or trimethylstannyl precursor., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Background: Transcranial direct current stimulation (tDCS) promotes recovery after stroke in humans. The underlying mechanisms, however, remain to be elucidated. Animal models suggest tDCS effects on neuroinflammation, stem cell proliferation, neurogenesis, and neural plasticity., Objective: In a longitudinal study, we employed tDCS in the subacute and chronic phase after experimental focal cerebral ischemia in mice to explore the relationship between functional recovery and cellular processes., Methods: Mice received photothrombosis in the right motor cortex, verified by Magnetic Resonance Imaging. A composite neuroscore quantified subsequent functional deficits. Mice received tDCS daily: either 5 sessions from day 5 to 9, or 10 sessions with days 12 to 16 in addition. TDCS with anodal or cathodal polarity was compared to sham stimulation. Further imaging to assess proliferation and neuroinflammation was performed by immunohistochemistry at different time points and Positron Emission Tomography at the end of the observation time of 3 weeks., Results: Cathodal tDCS at 198 kC/m 2 (220 A/m 2 ) between days 5 and 9 accelerated functional recovery, increased neurogenesis, decreased microglial activation, and mitigated CD16/32-expression associated with M1-phenotype. Anodal tDCS exerted similar effects on neurogenesis and microglial polarization but not on recovery of function or microglial activation. TDCS on days 12 to 16 after stroke did not induce any further effects, suggesting that the therapeutic time window was closed by then., Conclusion: Overall, data suggest that non-invasive neuromodulation by tDCS impacts neurogenesis and microglial activation as critical cellular processes influencing functional recovery during the early phase of regeneration from focal cerebral ischemia.

Brains are among the most energetically costly tissues in the mammalian body. 1 This is predominantly caused by expensive neurons with high glucose demands. 2 Across mammals, the neuronal energy budget appears to be fixed, possibly posing an evolutionary constraint on brain growth. 3-6 Compared to similarly sized mammals, birds have higher numbers of neurons, and this advantage conceivably contributes to their cognitive prowess. 7 We set out to determine the neuronal energy budget of birds to elucidate how they can metabolically support such high numbers of neurons. We estimated glucose metabolism using positron emission tomography (PET) and 2-[ 18 F]fluoro-2-deoxyglucose ([ 18 F]FDG) as the radiotracer in awake and anesthetized pigeons. Combined with kinetic modeling, this is the gold standard to quantify cerebral metabolic rate of glucose consumption (CMR glc ). 8 We found that neural tissue in the pigeon consumes 27.29 ± 1.57 μmol glucose per 100 g per min in an awake state, which translates into a surprisingly low neuronal energy budget of 1.86 × 10 -9  ± 0.2 × 10 -9 μmol glucose per neuron per minute. This is approximately 3 times lower than the rate in the average mammalian neuron. 3 The remarkably low neuronal energy budget explains how pigeons, and possibly other avian species, can support such high numbers of neurons without associated metabolic costs or compromising neuronal signaling. The advantage in neuronal processing of information at a higher efficiency possibly emerged during the distinct evolution of the avian brain., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Recently, a protocol for radiolabeling of aryl fluorosulfates ("SuFEx click radiolabeling") using ultrafast 18 F/ 19 F isotopic exchange has been reported. Although promising, the original procedure turned out to be rather inefficient. However, systematic optimization of the reaction parameters allowed for development of a robust method for SuFEx radiolabeling which obviates the need for azeotropic drying, base addition and HPLC purification. The developed protocol enabled efficient 18 F-fluorination of low nanomolar amounts of aryl fluorosulfates in highly diluted solution (micromolar concentrations). It was successfully used to prepare a series of 29 18 F-fluorosulfurylated phenols - including modified ezetimibe, α-tocopherol and etoposide, the two tyrosine derivatives Boc-Tyr([ 18 F]FS)-OMe and H-Tyr([ 18 F]FS)-OMe, the FAP-specific ligand [ 18 F]FS-UAMC1110, and the DPA-714 analog [ 18 F]FS-DPA - in fair to excellent yields. Preliminary evaluation demonstrated sufficient in vivo stability of radiofluorinated electron rich or neutral {Boc-Tyr([ 18 F]FS)-OMe), H-Tyr([ 18 F]FS)-OMe and [ 18 F]FS-DPA} aryl fluorosulfates. Furthermore, [ 18 F]FS-DPA was identified as a promising tracer for visualization of TSPO expression., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Cerebral glucose hypometabolism is a typical hallmark of Alzheimer's disease (AD), usually associated with ongoing neurodegeneration and neuronal dysfunction. However, underlying pathological processes are not fully understood and reproducibility in animal models is not well established. The aim of the present study was to investigate the regional interrelation of glucose hypometabolism measured by [ 18 F]FDG positron emission tomography (PET) with various molecular targets of AD pathophysiology using the PET tracers [ 18 F]PI-2620 for tau deposition, [ 18 F]DPA-714 for TSPO expression associated with neuroinflammation, and [ 18 F]UCB-H for synaptic density in a transgenic tauopathy mouse model. Seven-month-old rTg4510 mice (n = 8) and non-transgenic littermates (n = 8) were examined in a small animal PET scanner with the tracers listed above. Hypometabolism was observed throughout the forebrain of rTg4510 mice. Tau pathology, increased TSPO expression, and synaptic loss were co-localized in the cortex and hippocampus and correlated with hypometabolism. In the thalamus, however, hypometabolism occurred in the absence of tau-related pathology. Thus, cerebral hypometabolism was associated with two regionally distinct forms of molecular pathology: (1) characteristic neuropathology of the Alzheimer-type including synaptic degeneration and neuroinflammation co-localized with tau deposition in the cerebral cortex, and (2) pathological changes in the thalamus in the absence of other markers of AD pathophysiology, possibly reflecting downstream or remote adaptive processes which may affect functional connectivity. Our study demonstrates the feasibility of a multitracer approach to explore complex interactions of distinct AD-pathomechanisms in vivo in a small animal model. The observations demonstrate that multiple, spatially heterogeneous pathomechanisms can contribute to hypometabolism observed in AD mouse models and they motivate future longitudinal studies as well as the investigation of possibly comparable pathomechanisms in human patients., (© 2022. The Author(s).)

The short half-life of existing prostate-specific membrane antigen (PSMA) tracers limits their time for internalization into tumor cells after injection, which is an essential prerequisite for robust detection of tumor lesions with low PSMA expression on PET/CT scans. Because of its longer half-life, the 89 Zr-labeled ligand 89 Zr-PSMA-DFO allows acquisition of PET scans up to 6 d after injection, thereby overcoming the above limitation. We investigated whether 89 Zr-PSMA-DFO allowed more sensitive detection of weak PSMA-positive prostate cancer lesions. Methods: We selected 14 prostate cancer patients with biochemical recurrence who exhibited no PSMA-positive lesions on a PET scan acquired with existing PSMA tracers ( 68 Ga-PSMA-11, 18 F-JK-PSMA-7). Within 5 wk after the negative scan result, we obtained a second PSMA PET scan using 89 Zr-PSMA-DFO (117 ± 16 MBq, PET acquisition within 6 d of injection). Results: 89 Zr-PSMA-DFO detected 15 PSMA-positive lesions in 8 of 14 patients, who had a PET-negative reading of their initial PET scans with existing tracers. In these 8 patients, the new scans revealed localized recurrence of disease (3/8), metastases in lymph nodes (3/8), or lesions at distant sites (2/8). On the basis of these results, patients received lesion-targeted radiotherapies (5/8), androgen deprivation therapies (2/8), or no therapy (1/8). The plausibility of 14 of 15 lesions was supported by histology, clinical follow-up after radiotherapy, or subsequent imaging. Furthermore, comparison of the 15 89 Zr-PSMA-DFO-positive lesions with their correlates on the original PET scan revealed that established tracers exhibited mild accumulation in 7 of 15 lesions; however, contrast-to-noise ratios were too low for robust detection of these lesions (contrast-to-noise ratios, 2.4 ± 3.7 for established tracers vs. 10.2 ± 8.5 for 89 Zr-PSMA-DFO, P = 0.0014). The SUV max of the 15 89 Zr-PSMA-DFO-positive lesions (11.5 ± 5.8) was significantly higher than the SUV max on the original PET scans (4.7 ± 2.8, P = 0.0001). Kidneys were the most exposed organ, with doses of 3.3 ± 0.7 mGy/MBq. The effective dose was 0.15 ± 0.04 mSv/MBq. Conclusion: In patients with weak PSMA expression, a longer period of time might be needed for ligand internalization than that offered by existing PSMA tracers to make lesions visible on PET/CT scans. Hence, 89 Zr-PSMA-DFO might be of significant benefit to patients in whom the search for weak PSMA-positive lesions is challenging. Radiation exposure should be weighed against the potential benefit of metastasis-directed therapy or salvage radiotherapy, which we initiated in 36% (5/14) of our patients based on their 89 Zr-PSMA-DFO PET scans., (© 2022 by the Society of Nuclear Medicine and Molecular Imaging.)

Degradation products of the essential amino acid tryptophan (Trp) are important signaling molecules in the mammalian brain. Trp is metabolized either through the kynurenine pathway or enters serotonin and melatonin syntheses. The aim of the present work was to examine the potential of the novel PET tracer 7-[ 18 F]fluorotryptophan ([ 18 F]FTrp) to visualize all three pathways in a unilateral 6-OHDA rat model. [ 18 F]FDOPA-PET scans were performed in nine 6-OHDA-injected and six sham-operated rats to assess unilateral dopamine depletion severity four weeks after lesion placement. Afterwards, 7-[ 18 F]FTrp-PET scans were conducted at different timepoints up to seven months after 6-OHDA injection. In addition, two 6-OHDA-injected rats were examined for neuroinflammation using [ 18 F]DAA1106-PET. 7-[ 18 F]FTrp-PET showed significantly increased tracer uptake at the 6-OHDA injection site which was negatively correlated to time after lesion placement. Accumulation of [ 18 F]DAA1106 at the injection site was increased as well, suggesting that 7-[ 18 F]FTrp uptake in this region may reflect kynurenine pathway activity associated with inflammation. Bilaterally in the dorsal hippocampus, 7-[ 18 F]FTrp uptake was significantly decreased and was inversely correlated to dopamine depletion severity, indicating that it reflects reduced serotonin synthesis. Finally, 7-[ 18 F]FTrp uptake in the pineal gland was significantly increased in relation with dopamine depletion severity, providing evidence that melatonin synthesis is increased in the 6-OHDA rat model. We conclude that 7-[ 18 F]FTrp is able to detect alterations in both serotonin/melatonin and kynurenine metabolic pathways, and can be applied to visualize pathologic changes related to neurodegenerative processes., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Purpose: We present here a Zr-89-labeled inhibitor of prostate-specific membrane antigen (PSMA) as a complement to the already established F-18- or Ga-68-ligands., Procedures: The precursor PSMA-DFO (ABX) was used for Zr-89-labeling. This is not an antibody, but a peptide analogue of the precursor for the production of [ 177 Lu]Lu-PSMA-617. The ligand [ 89 Zr]Zr-PSMA-DFO was compared with [ 68 Ga]Ga-PSMA-11 and [ 18 F]F-JK-PSMA-7 in vitro by determination of the K d value, cellular uptake, internalization in LNCaP cells, biodistribution studies with LNCaP prostate tumor xenografts in mice, and in vivo by small-animal PET imaging in LNCaP tumor mouse models. A first-in-human PET was performed with [ 89 Zr]Zr-PSMA-DFO on a patient presenting with a biochemical recurrence after brachytherapy and an ambiguous intraprostatic finding with [ 18 F]F-JK-PSMA-7 but histologically benign cells in a prostate biopsy 7 months previously., Results: [ 89 Zr]Zr-PSMA-DFO was prepared with a radiochemical purity ≥ 99.9% and a very high in vitro stability for up to 7 days at 37 °C. All radiotracers showed similar specific cellular binding and internalization, in vitro and comparable tumor uptake in biodistribution experiments during the first 5 h. The [ 89 Zr]Zr-PSMA-DFO achieved significantly higher tumor/background ratios in LNCaP tumor xenografts (tumor/blood: 309 ± 89, tumor/muscle: 450 ± 38) after 24 h than [ 68 Ga]Ga-PSMA-11 (tumor/blood: 112 ± 57, tumor/muscle: 58 ± 36) or [ 18 F]F-JK-PSMA-7 (tumor/blood: 175 ± 30, tumor/muscle: 114 ± 14) after 4 h (p < 0.01). Small-animal PET imaging demonstrated in vivo that tumor visualization with [ 89 Zr]Zr-PSMA-DFO is comparable to [ 68 Ga]Ga-PSMA-11 or [ 18 F]F-JK-PSMA-7 at early time points (1 h p.i.) and that PET scans up to 48 h p.i. clearly visualized the tumor at late time points. A late [ 89 Zr]Zr-PSMA-DFO PET scan on a patient with biochemical recurrence (BCR) had demonstrated intensive tracer accumulation in the right (SUV max 13.25, 48 h p.i.) and in the left prostate lobe (SUV max 9.47), a repeat biopsy revealed cancer cells on both sides., Conclusion: [ 89 Zr]Zr-PSMA-DFO is a promising PSMA PET tracer for detection of tumor areas with lower PSMA expression and thus warrants further clinical evaluation., (© 2021. The Author(s).)

Purpose: The preclinical evaluation of 3-l- and 3-d-[ 18 F]FPhe in comparison to [ 18 F]FET, an established tracer for tumor imaging., Methods: In vitro studies were conducted with MCF-7, PC-3, and U87 MG human tumor cell lines. In vivo µPET studies were conducted in healthy rats with/without the inhibition of peripheral aromatic l-amino acid decarboxylase by benserazide pretreatment ( n = 3 each), in mice bearing subcutaneous MCF-7 or PC-3 tumor xenografts ( n = 10), and in rats bearing orthotopic U87 MG tumor xenografts ( n = 14). Tracer accumulation was quantified by SUV max , SUV mean and tumor-to-brain ratios (TBrR)., Results: The uptake of 3-l-[ 18 F]FPhe in MCF-7 and PC-3 cells was significantly higher relative to [ 18 F]FET. The uptake of all three tracers was significantly reduced by the suppression of amino acid transport systems L or ASC. 3-l-[ 18 F]FPhe but not 3-d-[ 18 F]FPhe exhibited protein incorporation. In benserazide-treated healthy rats, brain uptake after 42-120 min was significantly higher for 3-d-[ 18 F]FPhe vs. 3-l-[ 18 F]FPhe. [ 18 F]FET showed significantly higher uptake into subcutaneous MCF-7 tumors (52-60 min p.i.), while early uptake into orthotopic U87 MG tumors was significantly higher for 3-l-[ 18 F]FPhe (SUV max : 3-l-[ 18 F]FPhe, 107.6 ± 11.3; 3-d-[ 18 F]FPhe, 86.0 ± 4.3; [ 18 F]FET, 90.2 ± 7.7). Increased tumoral expression of LAT1 and ASCT2 was confirmed immunohistologically., Conclusion: Both novel tracers enable accurate tumor delineation with an imaging quality comparable to [ 18 F]FET.

Alcohol-dependent patients commonly show impairments in executive functions that facilitate craving and can lead to relapse. However, the molecular mechanisms leading to executive dysfunction in alcoholism are poorly understood, and new effective pharmacological treatments are desired. Here, using a bidirectional neuromodulation approach, we demonstrate a causal link between reduced prefrontal mGluR2 function and both impaired executive control and alcohol craving. A neuron-specific prefrontal mGluR2 knockdown in rats generated a phenotype of reduced cognitive flexibility and excessive alcohol seeking. Conversely, virally restoring prefrontal mGluR2 levels in alcohol-dependent rats rescued these pathological behaviors. In the search for a pharmacological intervention with high translational potential, psilocybin was capable of restoring mGluR2 expression and reducing relapse behavior. Last, we propose a FDG-PET biomarker strategy to identify mGluR2 treatment-responsive individuals. In conclusion, we identified a common molecular pathological mechanism for both executive dysfunction and alcohol craving and provided a personalized mGluR2 mechanism-based intervention strategy for medication development for alcoholism.

Selective inhibition of glycine transporter 1 (GlyT1) has emerged as a potential approach to alleviate N -methyl-d-aspartate receptor (NMDAR) hypofunction in patients with schizophrenia and cognitive decline. ALX5407 is a potent and selective inhibitor of GlyT1 derived from the metabolic intermediate sarcosine ( N -methylglycine) that showed antipsychotic potential in a number of animal models. Whereas clinical application of ALX5407 is limited by adverse effects on motor performance and respiratory function, a suitably radiolabeled drug could represent a promising PET tracer for the visualization of GlyT1 in the brain. Herein, [ 18 F]ALX5407 and the corresponding methyl ester, [ 18 F]ALX5406, were prepared by alcohol-enhanced copper mediated radiofluorination and studied in vitro in rat brain slices and in vivo in normal rats. [ 18 F]ALX5407 demonstrated accumulation consistent with the distribution of GlyT1 in in vitro autoradiographic studies but no brain uptake in μPET experiments in naı̈ve rats. In contrast, the methyl ester [ 18 F]ALX5406 rapidly entered the brain and was enzymatically transformed into [ 18 F]ALX5407, resulting in a regional accumulation pattern consistent with GlyT1 specific binding. We conclude that [ 18 F]ALX5406 is a promising and easily accessible PET probe for preclinical in vivo imaging of GlyT1 in the brain.

Drugs affecting neuromodulation, for example by dopamine or acetylcholine, take centre stage among therapeutic strategies in psychiatry. These neuromodulators can change both neuronal gain and synaptic plasticity and therefore affect electrophysiological measures. An important goal for clinical diagnostics is to exploit this effect in the reverse direction, i.e., to infer the status of specific neuromodulatory systems from electrophysiological measures. In this study, we provide proof-of-concept that the functional status of cholinergic (specifically muscarinic) receptors can be inferred from electrophysiological data using generative (dynamic causal) models. To this end, we used epidural EEG recordings over two auditory cortical regions during a mismatch negativity (MMN) paradigm in rats. All animals were treated, across sessions, with muscarinic receptor agonists and antagonists at different doses. Together with a placebo condition, this resulted in five levels of muscarinic receptor status. Using a dynamic causal model - embodying a small network of coupled cortical microcircuits - we estimated synaptic parameters and their change across pharmacological conditions. The ensuing parameter estimates associated with (the neuromodulation of) synaptic efficacy showed both graded muscarinic effects and predictive validity between agonistic and antagonistic pharmacological conditions. This finding illustrates the potential utility of generative models of electrophysiological data as computational assays of muscarinic function. In application to EEG data of patients from heterogeneous spectrum diseases, e.g. schizophrenia, such models might help identify subgroups of patients that respond differentially to cholinergic treatments. SIGNIFICANCE STATEMENT: In psychiatry, the vast majority of pharmacological treatments affect actions of neuromodulatory transmitters, e.g. dopamine or acetylcholine. As treatment is largely trial-and-error based, one of the goals for computational psychiatry is to construct mathematical models that can serve as "computational assays" and infer the status of specific neuromodulatory systems in individual patients. This translational neuromodeling strategy has great promise for electrophysiological data in particular but requires careful validation. The present study demonstrates that the functional status of cholinergic (muscarinic) receptors can be inferred from electrophysiological data using dynamic causal models of neural circuits. While accuracy needs to be enhanced and our results must be replicated in larger samples, our current results provide proof-of-concept for computational assays of muscarinic function using EEG., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2021. Published by Elsevier Inc.)

Background: Knowledge about the neuroinflammatory state during months after sudden cardiac arrest is scarce. Neuroinflammation is mediated by cells that express the 18 kDa translocator protein (TSPO). We determined the time course of TSPO-expressing cells in a rat model of sudden cardiac arrest using longitudinal in vivo positron emission tomography (PET) imaging with the TSPO-specific tracer [18F]DAA1106 over a period of 6 months., Methods: Five male Sprague Dawley rats were resuscitated from 6 min sudden cardiac arrest due to ventricular fibrillation, three animals served as shams. PET measurements were performed on day 5, 8, 14, 90, and 180 after intervention. Magnetic resonance imaging was performed on day 140. Imaging was preceded by Barnes Maze spatial memory testing on day 3, 13, 90, and 180. Specificity of [18F]DAA1106 binding was confirmed by Iba-1 immunohistochemistry., Results: [18F]DAA1106 accumulated bilaterally in the dorsal hippocampus of all sudden cardiac arrest animals on all measured time points. Immunohistochemistry confirmed Iba-1 expressing cells in the hippocampal CA1 region. The number of Iba-1-immunoreactive objects per mm2 was significantly correlated with [18F]DAA1106 uptake. Additionally, two of the five sudden cardiac arrest rats showed bilateral TSPO-expression in the striatum that persisted until day 180. In Barnes Maze, the relative time spent in the target quadrant negatively correlates with dorsal hippocampal [18F]DAA1106 uptake on day 14 and 180., Conclusions: After sudden cardiac arrest, TSPO remains expressed over the long-term. Sustainable treatment options for neuroinflammation may be considered to improve cognitive functions after sudden cardiac arrest., Competing Interests: All other authors report no conflicts of interest., (Copyright © 2020 by the Shock Society.)

We report radiolabeling of thiol-containing substrates via Pd-catalyzed S-arylation with 2-[ 18 F]fluoro-5-iodopyridine, which is readily accessible using the "minimalist" radiofluorination method. The practicality of the procedure was confirmed by preparation of a novel PSMA-specific PET-tracer as well as labeling of glutathione, Aβ oligomer-binding RD2 peptide, bovine serum albumin and PSMA I&S.

Purpose: PSMA imaging is frequently used for monitoring of androgen deprivation therapy (ADT) in prostate cancer. In a previous study, [ 18 F]-JK-PSMA-7 exhibited favorable properties for tumor localization after biochemical recurrence. In this retrospective study, we evaluated the performance of [ 18 F]-JK-PSMA-7 under ADT., Procedures: We examined the performance of [ 18 F]-JK-PSMA-7 in 70 patients (first cohort) with increasing or detectable PSA values under ADT (PSA < 2 ng/ml for 21/70 patients). We further analyzed 58 independent patients with PSA levels < 2 ng/ml under ADT, who were imaged with [ 68 Ga]PSMA-11 or [ 18 F]DCFPyL (second cohort). Finally, we compared detection rates between [ 18 F]-JK-PSMA-7, [ 68 Ga]PSMA-11, and [ 18 F]DCFPyL., Results: In the first cohort, we detected [ 18 F]-JK-PSMA-7-positive lesions in 63/70 patients. In patients with PSA levels ≥ 2 ng/ml, the detection rate was 100 % (49/49). In patients with PSA < 2 ng/ml, the detection rate was significantly lower (66.7 %, 14/21, p = 9.7 × 10 -5 ) and dropped from 85.7 % (12/14, PSA levels between 0.3 and 2.0 ng/ml) to 28.6 % (2/7) for PSA levels < 0.3 ng/ml (p = 1.73 × 10 -2 ). In the second cohort (PSA < 2 ng/ml), the detection rate was 79.3 % (46/58) for [ 68 Ga]PSMA-11 or [ 18 F]DCFPyL. Again, the detection rate was significantly higher (p = 1.1 × 10 -2 ) for patients with PSA levels between 0.3 and 2.0 ng/ml (87.0 %, 40/46) relative to those with PSA levels < 0.3 ng/ml (50 %, 6/12). No significant difference was found between [ 18 F]-JK-PSMA-7 and [ 68 Ga]PSMA-11 or [ 18 F]DCFPyL in patients with PSA levels < 2 ng/ml (p = 0.4295)., Conclusion: [ 18 F]-JK-PSMA-7 PET showed a high detection rate in patients with PSA levels ≥ 0.3 ng/ml under ADT. The lower PSA threshold of 0.3 ng/ml for high detection rates was consistent across the three PSMA ligands. Thus, PSMA imaging is suitable for clinical follow-up of patients with increasing PSA levels under ADT.

Objective. This study aimed at investigating a novel fully implantable deep brain stimulation (DBS) system and its ability to modulate brain metabolism and behavior through subthalamic nucleus (STN) stimulation in a hemiparkinsonian rat model. Approach. Twelve male rats were unilaterally lesioned with 6-hydroxydopamine in the medial forebrain bundle and received a fully implantable DBS system aiming at the ipsilesional STN. Each rat underwent three cylinder tests to analyze front paw use: a PRE test before any surgical intervention, an OFF test after surgery but before stimulation onset and an ON test under DBS. To visualize brain glucose metabolism in the awake animal, two [ 18 F]FDG scans were conducted in the OFF and ON condition. At least 4 weeks after surgery, an [ 18 F]FDOPA scan was used to check for dopaminergic integrity. Main results. In general, STN DBS increased [ 18 F]FDG uptake ipsilesionally and decreased it contralesionally. More specifically, bilateral orbitofrontal cortex, ipsilateral caudate putamen, sensorimotor cortex and nucleus accumbens showed significantly higher tracer uptake in ON compared to OFF condition. Contralateral cingulate and secondary motor cortex, caudate putamen, amygdala, hippocampus, retrosplenial granular cortex, superior colliculus, and parts of the cerebellum exhibited significantly higher [ 18 F]FDG uptake in the OFF condition. On the behavioral level, stimulation was able improve use of the contralesional affected front paw suggesting an effective stimulation produced by the implanted system. Significance. The fully implantable stimulation system developed by us and presented here offers the output of arbitrary user-defined waveforms, patterns and stimulation settings and allows tracer accumulation in freely moving animals. It is therefore a suitable device for implementing behavioral PET studies. It contributes immensely to the possibilities to characterize and unveil the effects and mechanisms of DBS offering valuable clues for future improvements of this therapy., (© 2021 IOP Publishing Ltd.)

Dnmt3a2, a de novo DNA methyltransferase, is induced by neuronal activity and participates in long-term memory formation with the increased expression of synaptic plasticity genes. We wanted to determine if Dnmt3a2 with its partner Dnmt3L may influence motor behavior via the dopaminergic system. To this end, we generated a mouse line, Dnmt3a2/3L Dat / wt , with dopamine transporter (DAT) promotor driven Dnmt3a2/3L overexpression. The mice were studied with behavioral paradigms (e.g., cylinder test, open field, and treadmill), brain slice patch clamp recordings, ex vivo metabolite analysis, and in vivo positron emission tomography (PET) using the dopaminergic tracer 6-[ 18 F]FMT. The results showed that spontaneous activity and exercise performance were enhanced in Dnmt3a2/3L Dat / wt mice compared to Dnmt3a2/3L wt / wt controls. Dopaminergic substantia nigra pars compacta neurons of Dnmt3a2/3L Dat / wt animals displayed a higher fire frequency and excitability. However, dopamine concentration was not increased in the striatum, and dopamine metabolite concentration was even significantly decreased. Striatal 6-[ 18 F]FMT uptake, reflecting aromatic L-amino acid decarboxylase activity, was the same in Dnmt3a2/3L Dat / wt mice and controls. [ 18 F]FDG PET showed that hypothalamic metabolic activity was tightly linked to motor behavior in Dnmt3a2/3L Dat / wt mice. Furthermore, dopamine biosynthesis and motor-related metabolic activity were correlated in the hypothalamus. Our findings suggest that Dnmt3a2/3L, when overexpressed in dopaminergic neurons, modulates motor performance via activation of the nigrostriatal pathway. This does not involve increased dopamine synthesis.

A general protocol for the preparation of 18F-labeled AAAs and α-methyl-AAAs applying alcohol-enhanced Cu-mediated radiofluorination of Bpin-substituted chiral complexes using Ni/Cu-BPX templates as double protecting groups is reported. The chiral auxiliaries are easily accessible from commercially available starting materials in a few synthetic steps. The versatility of the method was demonstrated by the high-yielding preparation of a series of [18F]F-AAAs and the successful implementation of the protocol into automated radiosynthesis modules.

18 F-prostate-specific membrane antigen (PSMA)-1007 is excreted mainly through the liver. We benchmarked the performance of 18 F-PSMA-1007 against 3 renally excreted PSMA tracers. Methods: Among 668 patients, we selected 27 in whom PET/CT results obtained with 68 Ga-PSMA-11, 18 F-DCFPyL (2-(3-(1-carboxy-5-[(6-[ 18 F]fluoro-pyridine-3-carbonyl)-amino]-pentyl)-ureido)-pentanedioic acid), or 18 F-JK-PSMA-7 (JK, Juelich-Koeln) were interpreted as equivocal or negative or as oligometastatic disease (PET-1). Within 3 wk, a second PET scan with 18 F-PSMA-1007 was performed (PET-2). The confidence in the interpretation of PSMA-positive locoregional findings was scored on a 5-point scale, first in routine diagnostics (reader 1) and then by an independent second evaluation (reader 2). Discordant PSMA-positive skeletal findings were examined by contrast-enhanced MRI. Results: For both readers, 18 F-PSMA-1007 facilitated the interpretability of 27 locoregional lesions. In PET-2, the clinical readout led to a significantly lower number of equivocal locoregional lesions ( P = 0.024), and reader 2 reported a significantly higher rate of suspected lesions that were falsely interpreted as probably benign in PET-1 ( P = 0.023). Exclusively in PET-2, we observed a total of 15 PSMA-positive spots in the bone marrow of 6 patients (22%). None of the 15 discordant spots had a morphologic correlate on the corresponding CT scan or on the subsequent MRI scan. Thus, 18 F-PSMA-1007 exhibits a significantly higher rate of unspecific medullary spots ( P = 0.0006). Conclusion: 18 F-PSMA-1007 may increase confidence in interpreting small locoregional lesions adjacent to the urinary tract but may decrease the interpretability of skeletal lesions., (© 2020 by the Society of Nuclear Medicine and Molecular Imaging.)

Based on the contribution of the endocannabinoid system to the pathophysiology of schizophrenia, the primary pro-psychotic ingredient of Cannabis sativa, Δ-9-tetrahydrocannabinol (Δ-9-THC), is used in preclinical as well as clinical research to mimic schizophrenia-like symptoms. While it is common to administer lipid-based formulations of Δ-9-THC in human studies orally, intraperitoneal injections of water-based solutions are used in animal models. Because of the poor water solubility of Δ-9-THC, solubilizers such as ethanol and/or emulsifiers are needed for these preparations. In order to test whether a lipid-based solvent would be superior over a water-based vehicle in rats, we compared the effects on locomotor activity and prepulse inhibition (PPI) of the acoustic startle reaction, as well as pharmacokinetic data obtained from rats' serum and brain tissue samples. Up to 50 mg/kg Δ-9-THC in the lipid-based formulation was not able to induce any behavioral alterations, while already 5 mg/kg of the water-based Δ-9-THC preparation significantly reduced locomotor activity. This also induced a small but significant PPI reduction, which was prepulse intensity dependent. Interestingly, the reflexive motor response to the startle stimulus was not affected by the water-based Δ-9-THC solution. Analysis of serum and brain Δ-9-THC levels by high-performance liquid chromatography/mass spectrometry revealed that although the final concentration reached in the brain was comparable for both pharmaceutical preparations, the water-based formulation achieved a faster kinetic. We, therefore, conclude that the slope of the Δ-9-THC concentration-time curve and the resulting cannabinoid receptor type 1 activation per time unit are responsible for the induction of behavioral alterations., (© 2019 Society for the Study of Addiction.)

In preclinical trials, the recently developed tracer 2-methoxy- 18 F-DCFPyL ( 18 F-JK-prostate-specific membrane antigen [PSMA]-7) has shown favorable properties regarding clinical performance and radiochemical accessibility. The aim of this study was to evaluate the clinical utility of 18 F-JK-PSMA-7 for PET/CT imaging of patients with prostate cancer. Methods: In an Institutional Review Board-approved pilot study, the initial clinical utility of PET/CT imaging with 18 F-JK-PSMA-7 was directly compared with 68 Ga-PSMA-11 PET/CT in a group of 10 patients with prostate cancer. The 2 PSMA tracers were administered to each patient less than 3 wk apart. Next, we analyzed the data of 75 consecutive patients who had undergone clinical 18 F-JK-PSMA-7 PET/CT imaging for tumor localization of biochemical recurrence (BCR). Results: The pilot study in 10 patients who were examined with both PSMA tracers demonstrated that 18 F-JK-PSMA-7 was at least equivalent to 68 Ga-PSMA-11. All unequivocally 68 Ga-PSMA-11-positive lesions could be also detected using 18 F-JK-PSMA-7, and in 4 patients additional suspected PSMA-positive lesions were identified (1 patient changed from PSMA-negative to PSMA-positive). In patients with BCR (after prostatectomy or radiotherapy), the capacity of 18 F-JK-PSMA-7 PET/CT to detect at least one PSMA-positive lesion was 84.8%. The prostate-specific antigen (PSA)-stratified detection rate of 18 F-JK-PSMA-7 after prostatectomy varied among 54.5% (6/11 patients; PSA < 0.5 μg/L), 87.5% (14/16 patients; PSA 0.5-2 μg/L), and 90.9% (20/22 patients; PSA > 2 μg/L). Conclusion: The tracer 18 F-JK-PSMA-7 was found to be safe and clinically useful. We demonstrated that 18 F-JK-PSMA-7 was not inferior when directly compared with 68 Ga-PSMA-11 in a pilot study but indeed identified additional PSMA-avid suspected lesions in oligometastasized patients with BCR. In a subsequent analysis of a clinical cohort of BCR patients, 18 F-JK-PSMA-7 was useful in tumor localization. 18 F-JK-PSMA-7 is recommended for future prospective trials., (© 2020 by the Society of Nuclear Medicine and Molecular Imaging.)

Aim: We investigated the whole-body distribution and the radiation dosimetry of [ 18 F]-JK-PSMA-7, a novel 18 F-labeled PSMA-ligand for PET/CT imaging of prostate cancer., Methods: Ten patients with prostate cancer and biochemical recurrence or radiologic evidence of metastatic diseases were examined with 329-384 MBq (mean 359 ± 17 MBq) [ 18 F]-JK-PSMA-7. Eight sequential positron emission tomography (PET) scans were acquired from 20 min to 3 h after injection with IRB approval. The kidneys, liver, lungs, spleen, and salivary glands were segmented into volumes of interest using the QDOSE dosimetry software suite (ABX-CRO, Germany). Absorbed and effective dose were calculated using the ICRP-endorsed IDAC 1.0 package. The absorbed dose of the salivary glands was determined using the spherical model of OLINDA 1.1. PSMA-positive lesions were evaluated separately. Quantitative assessment of the uptake in suspicious lesions was performed by analysis of maximum (max) and peak SUV values. The gluteus maximus muscle (SUV mean ) served as a reference region for the calculation of tumor-to-background ratios (TBR's)., Results: Physiologic radiotracer accumulation was observed in the salivary and lacrimal glands, liver, spleen, and intestines, in a pattern resembling the distribution known from other PSMA-tracers with excretion via urinary and biliary pathways. The effective dose from [ 18 F]-JK-PSMA-7 for the whole body was calculated to be 1.09E-02 mGy/MBq. The highest radiation dose was observed in the kidneys (1.76E-01 mGy/MBq), followed by liver (7.61E-02 mGy/MBq), salivary glands (4.68E-02 mGy/MBq), spleen (1.89E-02 mGy/MBq), and lungs (1.10E-2 mGy/MBq). No adverse effects of tracer injection were observed. Six out of ten patients were scored as PSMA-positive. A total of 18 suspicious lesions were analyzed, which included six bone lesions, nine lymph nodes, and three local lesions within the prostate fossa. The values for the SUV max and SUV peak in the PSMA-positive lesions increased until 60 min p.i. and remained at this intensity in the PET/CT scans until 140 min. In the period between 170 and 200 min after injection, a further significant increase in SUV max and SUV peak within the PSMA-positive lesions was observed., Conclusions: The highest TBR of [ 18 F]-JK-PSMA-7 was found 3 h after injection. From the kinetically collected data, it can be concluded that this trend may also continue in the further course. The start of the PET/CT acquisition should be chosen as late as possible. The high uptake in suspicious lesions in terms of absolute SUV max and relative TBR values indicates potentially high sensitivity of the tracer for detection of prostate cancer manifestations.

Background: The recent implementation of PET with prostate specific membrane antigen (PSMA)-specific radiotracers into the clinical practice has resulted in the significant improvement of accuracy in the detection of prostate carcinoma (PCa). PSMA-expression in ganglia has been regarded as an important pitfall in prostate carcinoma-PET diagnostics but has not found any practical use for diagnosis or therapy., Methods: We explored this phenomenon and demonstrated the applicability of peripheral ganglia in healthy rats as surrogates for small PSMA positive lesions for the preclinical evaluation of diagnostic PCa PET probes. Healthy rats were measured with PET/CT using the tracers [ 18 F]DCFPyL, [Al 18 F]PSMA-11 and [ 68 Ga]PSMA-11. Sections of ganglia were stained with an anti-PSMA antibody. [ 18 F]DCFPyL uptake in ganglia was compared to that in LNCaP tumor xenografts in mice., Results: Whereas [ 18 F]DCFPyL and [ 68 Ga]PSMA-11 were stable in vivo and accumulated in peripheral ganglia, [Al 18 F]PSMA-11 suffered from fast in vivo deflourination resulting in high bone uptake. Ganglionic PSMA expression was confirmed by immunohistochemistry. [ 18 F]DCFPyL uptake and signal-to-noise ratio in the superior cervical ganglion was not significantly different from LNCaP xenografts., Conclusions: Our results demonstrated the non-inferiority of the novel model compared to conventionally used tumor xenografts in immune compromised rodents with regard to reproducibility and stability of the PSMA signal. Furthermore, the model involves less expense and efforts while it is permanently available and avoids tumor-growth associated animal morbidity and distress. To the best of our knowledge, this is the first tumor-free model suitable for the in vivo evaluation of tumor imaging agents.

Prostate-specific membrane antigen (PSMA), expressed by most prostate carcinomas (PCa), is a promising target for PCa imaging. The application of PSMA-specific 18 F-labeled PET probes such as 18 F-DCFPyL and 18 F-PSMA-1007 considerably improved the accuracy of PCa tumor detection. However, there remains a need for further improvements in sensitivity and specificity. The aim of this study was the development of highly selective and specific PSMA probes with enhanced imaging properties, in comparison with 18 F-DCFPyL, 18 F-PSMA-1007, and 68 Ga-PSMA-11. Methods: Eight novel 18 F-labeled PSMA ligands were prepared. Their cellular uptake in PSMA-positive LNCaP C4-2 and PSMA-negative PC-3 cells was compared with that of 18 F-DCFPyL. The most promising candidates were additionally evaluated by small-animal PET in healthy rats using PSMA-positive peripheral ganglia as a model for small PCa lesions. PET images of the ligand with the best outcome, 18 F-JK-PSMA-7, were compared with those of 18 F-DCFPyL, 18 F-PSMA-1007, and 68 Ga-PSMA-11 with respect to key image-quality parameters for the time frame 60-120 min. Results: Compared with 18 F-DCFPyL, 18 F-JK-PSMA-7 demonstrated increased PSMA-specific cellular uptake. Although target-to-background ratios of 18 F-DCFPyL and 18 F-PSMA-1007 were comparable, this parameter was higher for 18 F-JK-PSMA-7 and lower for 68 Ga-PSMA-11. Image acutance was significantly higher for 18 F-JK-PSMA-7 and 18 F-PSMA-1007 than for 18 F-DCFPyL and 68 Ga-PSMA-11. Image resolution was similar for all 4 tracers. 18 F-PSMA-1007 demonstrated significantly higher blood protein binding and bone uptake than the other tracers. Conclusion: 18 F-JK-PSMA-7 is a promising candidate for high-quality visualization of small PSMA-positive lesions. Excellent preclinical imaging properties justify further preclinical and clinical studies of this tracer., (© 2019 by the Society of Nuclear Medicine and Molecular Imaging.)

Deep brain stimulation (DBS) in the subthalamic nucleus (STN) has been successfully used for the treatment of advanced Parkinson's disease, although the underlying mechanisms are complex and not well understood. There are conflicting results about the effects of STN-DBS on neuronal activity of the striatum, and its impact on functional striatal connectivity is entirely unknown. We therefore investigated how STN-DBS changes cerebral metabolic activity in general and striatal connectivity in particular. We used ipsilesional STN stimulation in a hemiparkinsonian rat model in combination with [ 18 F]FDOPA-PET, [ 18 F]FDG-PET and metabolic connectivity analysis. STN-DBS reversed ipsilesional hypometabolism and contralesional hypermetabolism in hemiparkinsonian rats by increasing metabolic activity in the ipsilesional ventrolateral striatum and by decreasing it in the contralesional hippocampus and brainstem. Other STN-DBS effects were subject to the magnitude of dopaminergic lesion severity measured with [ 18 F]FDOPA-PET, e.g. activation of the infralimbic cortex was negatively correlated to lesion severity. Connectivity analysis revealed that, in healthy control animals, left and right striatum formed a bilateral functional unit connected by shared cortical afferents, which was less pronounced in hemiparkinsonian rats. The healthy striatum was metabolically connected to the ipsilesional substantia nigra in hemiparkinsonian rats only (OFF condition). STN-DBS (ON condition) established a new functional striatal network, in which interhemispheric striatal connectivity was strengthened, and both the dopamine-depleted and the healthy striatum were functionally connected to the healthy substantia nigra. We conclude that both unilateral dopamine depletion and STN-DBS affect the whole brain and alter complex interhemispheric networks., Competing Interests: Competing interestsBetween October 2017 and October 2018, L.T. received payments as a consultant for Medtronic Inc, Boston Scientific. L.T. received honoraria as a speaker at symposia sponsored by Bial, Zambon Pharma, UCB Schwarz Pharma, Desitin Pharma, Medtronic, Boston Scientific and Abbott. The institution of L.T., not L.T. personally, received funding from the Deutsche Forschungsgemeinschaft, the Bundesministerium für Bildung und Forschung and Deutsche Parkinson Vereinigung. Neither L.T. nor any member of his family holds stocks, stock options, patents or financial interests in any of the above-mentioned companies or their competitors. During the last 12 months, A.D. received payments as a consultant for the Deutsches Zentrum für Neurodegenerative Erkrankungen and General Electric (GE). He also received honoraria as a speaker at symposia sponsored by Siemens. The institution of A.D. received funding by Siemens, Lilly-Avid and Life Molecular Imaging. No other authors have received any funding from any institution, including personal relationships, interests, grants, employment, affiliations, patents, inventions, honoraria, consultancies, royalties, stock options/ownership, or expert testimony for the last 12 months., (© 2019. Published by The Company of Biologists Ltd.)

The nonlysosomal glucosylceramidase β2 (GBA2) catalyzes the hydrolysis of glucosylceramide to glucose and ceramide. Mutations in the human GBA2 gene have been associated with hereditary spastic paraplegia (HSP), autosomal-recessive cerebellar ataxia (ARCA), and the Marinesco-Sjögren-like syndrome. However, the underlying molecular mechanisms are ill-defined. Here, using biochemistry, immunohistochemistry, structural modeling, and mouse genetics, we demonstrate that all but one of the spastic gait locus #46 (SPG46)-connected mutations cause a loss of GBA2 activity. We demonstrate that GBA2 proteins form oligomeric complexes and that protein-protein interactions are perturbed by some of these mutations. To study the pathogenesis of GBA2-related HSP and ARCA in vivo , we investigated GBA2-KO mice as a mammalian model system. However, these mice exhibited a high phenotypic variance and did not fully resemble the human phenotype, suggesting that mouse and human GBA2 differ in function. Whereas some GBA2-KO mice displayed a strong locomotor defect, others displayed only mild alterations of the gait pattern and no signs of cerebellar defects. On a cellular level, inhibition of GBA2 activity in isolated cerebellar neurons dramatically affected F-actin dynamics and reduced neurite outgrowth, which has been associated with the development of neurological disorders. Our results shed light on the molecular mechanism underlying the pathogenesis of GBA2-related HSP and ARCA and reveal species-specific differences in GBA2 function in vivo ., (© 2019 Woeste et al.)

The short- and long-term success of intravascular stents depends on a proper re-endothelialisation after the intervention-induced endothelial denudation. The aim of this study was to evaluate the potential of in vivo molecular imaging of glutamate carboxypeptidase II (GCPII; identical with prostate-specific membrane antigen PSMA) expression as a marker of re-endothelialisation. Fifteen Sprague Dawley rats underwent unilateral balloon angioplasty of the common carotid artery (CCA). Positron emission tomography (PET) using the GCPII-targeting tracer [ 18 F]DCFPyL was performed after 5-21 days (scan 60-120 min post injection). In two animals, the GCPII inhibitor PMPA (23 mg/kg BW) was added to the tracer solution. After PET, both CCAs were removed, dissected, and immunostained with the GCPII specific antibody YPSMA-1. Difference of GCPII expression between both CCAs was established by PCR analysis. [ 18 F]DCFPyL uptake was significantly higher in the ipsilateral compared to the contralateral CCA with an ipsi-/contralateral ratio of 1.67 ± 0.39. PMPA blocked tracer binding. The selective expression of GCPII in endothelial cells of the treated CCA was confirmed by immunohistological staining. PCR analysis verified the site-specific GCPII expression. By using a molecular imaging marker of GCPII expression, we provide the first non-invasive in vivo delineation of re-endothelialisation after angioplasty.

Tryptophan and its metabolites are involved in different physiological and pathophysiological processes. Consequently, positron emission tomography (PET) tracers addressing tryptophan metabolic pathways should allow the detection of different pathologies like neurological disorders and cancer. Herein we report an efficient method for the preparation of fluorotryptophans labeled in different positions with 18 F and their biological evaluation. 4-7-[ 18 F]Fluorotryptophans ([ 18 F]FTrps) were prepared according to a modified protocol of alcohol-enhanced Cu-mediated radiofluorination in 30-53% radiochemical yields. In vitro experiments demonstrated high cellular uptake of 4-7-[ 18 F]FTrps in different tumor cell lines. 4, 5-, and 6-[ 18 F]FTrps, although stable in vitro, suffered from rapid in vivo defluorination. In contrast, 7-[ 18 F]FTrp demonstrated a high in vivo stability and enabled a clear delineation of serotonergic areas and melatonin-producing pineal gland in rat brains. Moreover 7-[ 18 F]FTrp accumulated in different tumor xenografts in a chick embryo CAM model. Thus, 7-[ 18 F]FTrp represents a highly promising PET probe for imaging of Trp metabolism.

Pathological cerebral aggregations of proteins are suggested to play a crucial role in the development of neurodegenerative disorders. For example, aggregation of the protein ß-amyloid in form of extracellular amyloid-plaques as well as intraneuronal depositions of the protein tau in form of neurofibrillary tangles represent hallmarks of Alzheimer's disease (AD). Recently, novel tracers for in vivo molecular imaging of tau-aggregates in the brain have been introduced, complementing existing tracers for imaging amyloid-plaques. Available data on these novel tracers indicate that the subject of Tau-PET may be of considerable complexity. On the one hand this refers to the various forms of appearance of tau-pathology in different types of neurodegenerative disorders. On the other hand, a number of hurdles regarding validation of these tracers still need to be overcome with regard to comparability and standardization of the different tracers, observed off-target/non-specific binding and quantitative interpretation of the signal. These issues will have to be clarified before systematic clinical application of this exciting new methodological approach may become possible. Potential applications refer to early detection of neurodegeneration, differential diagnosis between tauopathies and non-tauopathies and specific patient selection and follow-up in therapy trials., (Copyright © 2017. Published by Elsevier Inc.)

Background: In Parkinson's disease (PD), cerebral dopamine depletion is associated with PD subtype-specific metabolic patterns of hypo- and hypermetabolism. It has been hypothesised that hypometabolism reflects impairment, while hypermetabolism may indicate compensatory activity. In order to associate metabolic patterns with pathophysiological and compensatory mechanisms, we combined resting state [ 18 F]FDG-PET (to demonstrate brain metabolism in awake animals), [ 18 F]FDOPA-PET (dopamine depletion severity) and gait analysis in a unilateral 6-hydroxydopamine rat model., Results: We found unilateral nigro-striatal dopaminergic loss to decrease swing speed of the contralesional forelimb and stride length of all paws in association with depletion severity. Depletion severity was found to correlate with compensatory changes such as increased stance time of the other three paws and diagonal weight shift to the ipsilesional hind paw. [ 18 F]FDG-PET revealed ipsilesional hypo- and contralesional hypermetabolism; metabolic deactivation of the ipsilesional network needed for sensorimotor integration (hippocampus/retrosplenial cortex/lateral posterior thalamus) was solely associated with bradykinesia, but hypometabolism of the ipsilesional rostral forelimb area was related to both pathological and compensatory gait changes. Mixed effects were also found for hypermetabolism of the contralesional midbrain locomotor region, while contralesional striatal hyperactivation was linked to motor impairments rather than compensation., Conclusions: Our results indicate that ipsilesional hypo- and contralesional hypermetabolism contribute to both motor impairment and compensation. This is the first time when energy metabolism, dopamine depletion and gait analysis were combined in a hemiparkinsonian model. By experimentally increasing or decreasing compensational brain activity, its potential and limits can be further investigated.

Prepulse inhibition (PPI) is a neuropsychological process during which a weak sensory stimulus ("prepulse") attenuates the motor response ("startle reaction") to a subsequent strong startling stimulus. It is measured as a surrogate marker of sensorimotor gating in patients suffering from neuropsychological diseases such as schizophrenia, as well as in corresponding animal models. A variety of studies has shown that PPI of the acoustical startle reaction comprises three brain circuitries for: (i) startle mediation, (ii) PPI mediation, and (iii) modulation of PPI mediation. While anatomical connections and information flow in the startle and PPI mediation pathways are well known, spatial and temporal interactions of the numerous regions involved in PPI modulation are incompletely understood. We therefore combined [(18)F]fluoro-2-deoxyglucose positron-emission-tomography (FDG-PET) with PPI and resting state control paradigms in awake rats. A battery of subtractive, correlative as well as seed-based functional connectivity analyses revealed a default mode-like network (DMN) active during resting state only. Furthermore, two functional networks were observed during PPI: Metabolic activity in the lateral circuitry was positively correlated with PPI effectiveness and involved the auditory system and emotional regions. The medial network was negatively correlated with PPI effectiveness, i.e., associated with startle, and recruited a spatial/cognitive network. Our study provides evidence for two distinct neuronal networks, whose continuous interplay determines PPI effectiveness in rats, probably by either protecting the prepulse or facilitating startle processing. Discovering similar networks affected in neuropsychological disorders may help to better understand mechanisms of sensorimotor gating deficits and provide new perspectives for therapeutic strategies.

Background: Clinical data suggest that transcranial direct current stimulation (tDCS) may be used to facilitate rehabilitation after stroke. However, data are inconsistent and the neurobiological mechanisms underlying tDCS remain poorly explored, impeding its implementation into clinical routine. In the healthy rat brain, tDCS affects neural stem cells (NSC) and microglia. We here investigated whether tDCS applied after stroke also beneficially affects these cells, which are known to be involved in regeneration and repair., Methods: Focal cerebral ischemia was induced in rats by transient occlusion of the middle cerebral artery. Twenty-eight animals with comparable infarcts, as judged by magnetic resonance imaging, were randomized to receive a multi-session paradigm of either cathodal, anodal, or sham tDCS. Behaviorally, recovery of motor function was assessed by Catwalk. Proliferation in the NSC niches was monitored by Positron-Emission-Tomography (PET) employing the radiotracer 3'-deoxy-3'-[(18)F]fluoro-l-thymidine ([(18)F]FLT). Microglia activation was depicted with [(11)C]PK11195-PET. In addition, immunohistochemical analyses were used to quantify neuroblasts, oligodendrocyte precursors, and activation and polarization of microglia., Results: Anodal and cathodal tDCS both accelerated functional recovery, though affecting different aspects of motor function. Likewise, tDCS induced neurogenesis independently of polarity, while only cathodal tDCS recruited oligodendrocyte precursors towards the lesion. Moreover, cathodal stimulation preferably supported M1-polarization of microglia., Conclusions: TDCS acts through multifaceted mechanisms that far exceed its primary neurophysiological effects, encompassing proliferation and migration of stem cells, their neuronal differentiation, and modulation of microglia responses., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Inflammatory cells such as microglia need energy to exert their functions and to maintain their cellular integrity and membrane potential. Subsequent to cerebral ischemia, inflammatory cells infiltrate tissue with limited blood flow where neurons and astrocytes died due to insufficient supply with oxygen and glucose. Using dual tracer positron emission tomography (PET), we found that concomitant with the presence of inflammatory cells, transport and consumption of glucose increased up to normal levels but returned to pathological levels as soon as inflammatory cells disappeared. Thus, inflammatory cells established sufficient glucose supply to satisfy their energy demands even in regions with insufficient supply for neurons and astrocytes to survive. Our data suggest that neurons and astrocytes died from oxygen deficiency and inflammatory cells metabolized glucose non-oxidatively in regions with residual availability. As a consequence, glucose metabolism of inflammatory cells can mask metabolic deficits in neurodegenerative diseases. We further found that the PET tracer did not bind to inflammatory cells in severely hypoperfused regions and thus only a part of the inflammation was detected. We conclude that glucose consumption of inflammatory cells should be taken into account when analyzing disease-related alterations of local cerebral metabolism., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)